U.S. patent number 4,997,286 [Application Number 07/347,195] was granted by the patent office on 1991-03-05 for apparatus for measuring temperature using a sensor element.
This patent grant is currently assigned to Degussa AG. Invention is credited to Gustav W. Fehrenbach, Stefan Schmidt.
United States Patent |
4,997,286 |
Fehrenbach , et al. |
March 5, 1991 |
Apparatus for measuring temperature using a sensor element
Abstract
An apparatus for measuring temperature in a region of high
temperature is disclosed herein. The measuring apparatus includes a
sensor made from a fluorescent material, located within the region
of high temperature. The fluorescent decay time of the fluorescent
material is dependent upon the temperature of the fluorescent
material. A first optical waveguide is located within the high
temperature region and coupled to the sensor by means of a glass
solder. The first optical waveguide is coupled to a second optical
waveguide located outside the region of high temperature, and the
second optical waveguide is connected to a means for detecting and
evaluating the fluorescent radiation, also located outside the
region of high temperature. A source of excitation radiation is
used to cause the fluorescent material to fluoresce, and by
measuring the fluorescence decay time, the temperature within the
region can be determined.
Inventors: |
Fehrenbach; Gustav W. (Hanau,
DE), Schmidt; Stefan (Russelsheim, DE) |
Assignee: |
Degussa AG (Frankfurt,
DE)
|
Family
ID: |
25953043 |
Appl.
No.: |
07/347,195 |
Filed: |
May 4, 1989 |
Foreign Application Priority Data
|
|
|
|
|
May 12, 1988 [DE] |
|
|
8806290 |
Jun 24, 1988 [DE] |
|
|
8808168 |
|
Current U.S.
Class: |
374/131;
250/227.21; 374/161; 374/E11.017; 385/53; 385/95 |
Current CPC
Class: |
G01K
11/3213 (20130101); G02B 6/262 (20130101) |
Current International
Class: |
G02B
6/26 (20060101); G01K 11/32 (20060101); G01K
11/00 (20060101); G01N 021/04 (); G02B
006/255 () |
Field of
Search: |
;374/121,131,161
;250/227,231R,227.21 ;350/96.18,96.20,96.21 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Yasich; Daniel M.
Attorney, Agent or Firm: Beveridge, DeGrandi &
Weilacher
Claims
We claim:
1. An apparatus for measuring a temperature in a high temperature
region of greater than 200.degree. C. by measuring a fluorescence
decay time of a fluorescent material located within the region,
said apparatus comprising:
a sensor including said fluorescent material, said fluorescense
decay time of the fluorescent material depending upon the
temperature in the region where said sensor is located, whereby
said fluorescent material emits fluorescent radiation upon exposure
to an excitation radiation,
a first optical waveguide connected to said sensor by a glass
solder which is capable of withstanding temperatures greater than
200.degree. C., the thermal expansion coefficient of the first
optical waveguide and of the glass solder being approximately equal
to the thermal expansion coefficient of the sensor, so as to
provide an optically transparent connection therebetween, said
first optical waveguide being adapted to connect to a second
optical waveguide located outside of said region, said second
waveguide being adapted to be connected to a means for detecting
and evaluating the fluorescent radiation emitted by said
fluorescent material.
2. Apparatus according to claim 1, characterized in that the first
optical waveguide (14) connected to said sensor (10) comprises a
multi-component glass optical waveguide.
3. Apparatus according to claim 1, characterized in that the first
optical waveguide (14) connected to the sensor (10) and/or the
second optical waveguide (24) connected to said means for detecting
and evaluating is a flexible optical waveguide, wherein said means
for detecting and evaluating further includes a means for producing
an excitation radiation.
4. Apparatus according to claim 1, characterized in that the first
optical waveguide (14) connected tot he sensor (10) and/or the
second optical waveguide (24) connected to said means for detecting
and evaluating is a fibre optic, wherein said means for detecting
and evaluating further includes a means for producing an excitation
radiation.
5. Apparatus according to claim 1, characterized in that the first
and second optical waveguides (14, 24) are connected to one another
by plug-in elements (20,22) of a connector.
6. Apparatus according to claim 1, characterized in that the first
and second optical waveguides (14, 24) are connected to one another
by glue splice connections.
7. Apparatus according to claim 1, characterized in that the sensor
(10) is coated with a glass solder, the refractive index of which
is lower than that of the sensor.
8. Apparatus according to claim 1, characterized in that the
cross-section of the first optical waveguide (14) is adapted to
that of the element (10).
9. Apparatus according to claim 8, characterized in that the
cross-section of the sensor (10) is square.
10. Apparatus according to claim 9, characterized in that the edge
length of the cross-sectionally square sensor (10) corresponds to
the diameter of the first optical waveguide (14).
11. Apparatus according to claim 1, characterized in that the
second optical waveguide (24) has a lower attenuation than the
first optical waveguide.
12. The apparatus as defined in claim 1 wherein said sensor
includes Cr:YAG.
Description
The invention relates to an apparatus for measuring temperature
using a sensor element made from a photoluminescent material which
is connected by way of an optical waveguide optical system to a
device for producing an excitation radiation and for detecting and
evaluating received radiation.
The fluorescence decay period of the radiation of the
photoluminescent material is measured by apparatus of the type
described above. The fluorescence decay period is dependent upon
the prevailing temperature. To transmit the light energy, mostly
fibres made from quartz glass or synthetic material are used which
have very good transmission properties. Quartz has a relatively low
thermal expansion coefficient. Sensor elements suitable for high
temperatures, made from a material such as, for example, Cr: YAG,
on the other hand, have higher thermal expansion coefficients.
An optically transparent connection must be established between the
sensor element and the fibre optic. This optically transparent
connection is exposed to approximately the same temperatures as the
sensor element used to measure the temperatures. If it is only an
area of relatively low temperatures which the sensor element is
required to measure, an organic-based optical adhesive, e.g. an
epoxy resin, may be used to join the sensor element and the fibre
optic. A joint like this is not, however, suitable for continuous
operating temperatures in excess of 200.degree. C.
The aim of the invention is further to develop an apparatus of the
type mentioned initially so that higher temperatures do not result
in damage to the joint between the sensor element and a fibre optic
connected thereto.
This aim is achieved in accordance with the invention in that the
sensor element is fastened by means of glass solder to one end of
at least a first optical waveguide, that the glass solder and the
first optical waveguide have thermal expansion coefficients which
are adapted at least to the thermal expansion coefficients of the
sensor element, and that the other end of the first optical
waveguide in a region of low temperature is connected to a second
optical waveguide, e.g. standard optical waveguides made from
quartz glass, glass, synthetic material etc. In this apparatus, a
first optical waveguide, which is not made from quartz glass, is
used to effect a connection of high-temperature stability with the
sensor element. This intermediate transfer medium generally does
not have optical transmission properties for light energy which are
as good as quartz glass. Compared the second optical waveguide, the
intermediate transfer optical waveguide is substantially shorter
since it is only used in the high-temperature region. The fact that
the optical transmission properties of the intermediate transfer
optical waveguide are inferior is not therefore of any major
significance.
Preferably, the first optical waveguide connected to the sensor
element is made from a multi-component glass. This multi-component
glass, of a composition geared towards an appropriate thermal
expansion coefficient, may have approximately the same thermal
expansion coefficient as the sensor element and the glass solder
made, for example, from the same glass material. The joint, as
described above, between the sensor element and the first optical
waveguide made from the multi-component glass is easily capable of
withstanding temperatures of more than 200 .degree. C.
Reference is also made to a particularly advantageous further
development. The glass solder is used not merely to establish the
connection between the optical waveguide and the sensor element. If
a glass solder is used with a refractive index which is lower than
that of the sensor element and if this glass solder is used not
only at the joint but also to form a thin coating over the entire
sensor element (e.g. by immersion), then the sensor crystal too
becomes a protected optical waveguide. Dirt on the glass solder
surface then does not further dampen the signal. The glass solder
coating must, however, be at least several .mu.m thick.
It is advantageous if the first optical waveguide connected to the
sensor element and/or the second optical waveguide connected to a
device for producing an excitation radiation and for detecting and
evaluating received radiation is a flexible optional waveguide.
It is also possible for the first optical waveguide connected to
the sensor element and/or the second optical waveguide connected to
a device for producing an excitation radiation and of detecting and
evaluating received radiation to be a fibre optic.
The optical waveguides or fibre optics are preferably connected to
one another by means of plug-in elements of a connector. This type
of connection permits the sensor element with the optical fibre
made from multicomponent glass fastened thereon to be handled as a
independent unit. This unit can be connected to standard optical
waveguides such as optical fibres made from quartz glass of varying
length, thereby making its use very flexible.
The optical waveguides may also advantageously be connected to one
another by glue splice connections. A joint like this is
particularly cost-effective to produce.
The cross-sections of the materials at the joints have to be
adapted to one another. It may be expedient on production
engineering grounds to connect the optical waveguide not to a
cylindrical sensor element of the same diameter but to a sensor
element with a square crosssection. This entails adaptation of the
cross-section so that the edge length of the square cross-section
is equal to the diameter of the optical waveguide.
It may also be expedient to use optical waveguides with a slightly
different numerical aperture and somewhat varying core diameter. At
the cost of additional losses, a more stable coupling is thereby
achieved, which is therefore less susceptible to interference.
BRIEF DESCRIPTION OF DRAWING
Further details, advantages and features of the invention are
evident not only from the sub-claims, the features indicated in
them--individually and/or in combination--but also from the
following description of preferred embodiments as illustrated in
the single figure of drawing.
The drawing shows a sensor element (10) made from a
photolumicescent material such as, for example, Cr: YAG, one flat
side (12) of which abuts a flat face of a first optical waveguide
(14) made from a multi-component glass. At the edges of the face,
the first optical waveguide (14) is firmly joined by glass solder
(16) to the sensor element (10). The material of the optical
waveguide (14) and of the glass solder (16) is selected so that
their thermal expansion coefficients are equal or approximately
equal to the thermal expansion coefficient of the sensor element
(10). The sensor element (10) and the largest portion of the
optical waveguide (14) are located in chamber (18) in which a high
temperature prevails which is to be measured by the sensor element
(10).
The second face of the optical waveguide (14) is connected outside
of the chamber (18) to a plug-in element (20) of a connector for
optical waveguides. The other plug-in element (22) of the connector
is connected to one end of a second standard optical waveguide
(24), the other end of which is connected to a device (26) for
producing an excitation radiation and for detecting and evaluating
the radiation of the sensor element (10) fed back by way of the
first and second optical waveguides (14) and (24).
The device (26) measures the fluorescence decay period of the
radiation of the photoluminescent material of the sensor element
(10). The fluorescence decay period is dependant in a known manner
upon the temperature in the chamber (18).
The firm joint produced by the glass solder (16) between the sensor
element (10) and the first optical waveguide (14) can withstand
high temperatures of, e.g., more than 400.degree. C. The apparatus
illustrated in the drawing is therefore suitable for measuring high
temperatures. The sensor element (10) and the first optical
waveguide (14) in conjunction with the plug-in element (20) form an
independent unit which is connectible to second optical waveguides
(24) of varying length, depending upon the spatial conditions and
the distance between the chamber (18) and the device (26).
Instead of a detachable connector between the first and second
optical waveguides, the first optical waveguide may be connected to
the second optical waveguide by means of a less expensive glue
splice connection.
Instead of single optical waveguides, fibre optics may be used.
The plug-in elements (20), (22) and the glue splice connections are
suitable for temperatures up to around 100.degree. C., i.e. the
connections may be disposed outside of the chamber (18) but still
in its vicinity in order to keep the length of the first optical
waveguide (14) or the length of the fibre optics to a minimum. The
first optical waveguide (14) is used as a intermediate transfer
element between the sensor element (10) and the second optical
waveguide (24). Although the optical transmission properties of the
first optical waveguide (14) are inferior to those of the second
optical waveguide (24), this is not a particular disadvantage owing
to the shorter length of the first optical waveguide (14).
Finally, it should be mentioned that the sensor element (10) may of
course by provided with mechanical protection such as a sleeve,
protective tube, hinged cover, which may be made from any suitable,
temperature-resistant materials.
* * * * *